Nato is to deploy reconnaissance planes in Poland and Romania to monitor the Ukrainian crisis.

It gave the go-ahead for the flights on Monday, a Nato spokesman said.

"All Awacs (Airborne Warning and Control System) reconnaissance flights will take place solely over alliance territory," the official said.

It comes as Russia cements its control of Ukraine's Crimea ahead of Sunday's referendum to join Russia. Ukraine and the West say this is illegal.

Nato said the surveillance flights would "enhance the alliance's situational awareness".

Last week, the organisation said it was reviewing all co-operation with Russia and stepping up its engagement with the government in Kiev.